Mold chill



Patented Aug. 7, 1945 MOLD CHILL Marvin E. Gantz, Lakewood, Ohio,asslgnor to Aluminum Company of America, Pittsburgh, Pa, a corporationof Pennsylvania No Drawing. Application March 31, 1942, Serial No.437,089

3 Claims. (Cl. 22-188) This invention relates to the art of makingmolds, or parts thereof, of sand or similar material that will make afrangible mold or mold part, and it is especially concerned withprovidin chills for said molds or parts.

In making castings in sand molds or molds containing sand cores, it iswell recognized that the molten metal freezes relatively slowly in suchmolds as compared to the rate of freezing in an all metal mold. Inmaking some castings the rate of freezing is important, and the slowfreezing which normally occurs in a sand mold or in contact with a sandcore must be increased in order to avoid shrinkage, reduce the grainsize, and/or to increase the surface hardness of the casting. To thushasten the freezing rate in portions of the mold, it has been acommonpractice to embed blocks of metal in the sand mold or core. Such blocksof metal are referred to in the art as chills. The quantity cf'heat thatany chill will absorb and the rate at which the heat is absorbedconstitute what is herein referred to as chilling effect.

in certain parts, it is frequently necessary to provide specially shapedchills to conform to the contour of the casting. Such special chills areobviously expensive to make and maintain, to say nothing of the laborinvolved in positioning them in the mold. In some cases where chillshave been desired, it has been physically impossible to use blocksbecause of the size or location of the chill. This situation has led meto devise a new type of chili which can be molded to fit any desiredcontour or location as the mold or core is being made. the principalobject of my invention being the provision of a chillwhich is not onlyinitially moldable but which will provide a chill that performs the samefunction as the conventional type of metal block chills used heretofore.A particular object is to provide a moldable chill mixture which isadapted for use in green sand molds and may or may not be, hardenable atthe discretion of the foundryman. Another object is to provide a chillfor use in making light alloy castings.

My invention is predicated upon the discovery that a compositioncomprising an intimate mixture of small metal pellets and a suitablebinder is readily moldable, when properly tempered, prior to placementin a mold or core made of sand or similar material and yet can be hardened, if desired, at room temperature or at an elevated temperature,depending upon the character ofathe binder, with the result thata firmWhen castings are made that have a complicated shape and must be chilledchill body is produced which will not crumble incontact with the moltenmetal in the mold. The benefit derived from the use of such chills isreflected in a reduction in grain size and shrinkage and/or an increasein surface hardness of the casting as compared to the same casting madewithout the chills. B means of such a composition it is possible to usechills of varying size at any place in a sand mold or core, particularlyin locations where block chills cannot be employed such as in thinsections or tortuous passages, and also to make the chill body conformto the shape of the casting to be made in the mold. In some instances itmay even be desirable to make an entire core of the chill mixture. In noevent, however, does moldingsand form a part of the mixture because itreduces the chilling effect too greatly. The selection of the correctamount of chill for a given portion of a casting can be readilydetermined by the foundryman. After the casting has been formed in themold, the chill, together with the sand, can be readily broken away inthe usual manner. This is especially important in the removal of sandcores. The moldable mixture containing metal pellets, binder, andtempering medium may be referred to for purposes of convenience as agreen chill mixture while if the binder is of the hardening type, theresulting chill body may be referred to as, a hardened chill mixture.The improved chill which I have devised may be said to be characterizedby its initial moldability, i. e., its adaptability to being shapedduring the usual molding operations, its capability of being hardened,if desired, and a chilling effect similar to that of the metal blocksheretofore employed.

By a chilling effect similar to that of metal block chills, I mean thatthe chill composition herein described and claimed reduces the grainsize and shrinkage of the casting in the region where the chili isemployed as compared to the condition prevailing when no 'chill is used.In some cases the chilling may also cause an increase in the surfacehardness of the casting.

The term, harden, as used herein refer to the loss of moldability andsetting of a green chill mixture through evaporation of all or part ofthe tempering medium or through a change in the binder, or both, whichoccurs naturally on standing exposed to the atmosphere or by exposure toan elevated temperature prior to the time that the casting is poured inthe mold. The expression, chill mixture, without reference to greennessor hardness covers the chill mixture in both conditions.

Although the chill mixture herein described is adapted for use in moldsand cores employed in the casting of a large variety of metals andalloys, I have found it to be especially useful in making castings oflight metals, particularly those of magnesium and magnesium base alloys.The molds and cores where the chill mixture is used are generally madeof sand or similar material. The molds may be eith'erof the green or drytyp but the cores are usually baked prior to use. The baked cores may beused in so-called permanent molds'as well as in sand molds. The term,sand,

as used herein, is intended to cover not only sand itself, but also itsequivalents.

The metal portion of the chill mixture should consist of metal pelletswhich will not ruse at the temperature of the molten metal being cast inthe mold. A variety of metals may generally be so employed, but forpractical purposes a cheap metal having a high and rapid heat absorbingcapacity will generally be preferred, such as iron or copper. Anotherconsideration which affects the selection of the kind of metal pelletsemployed in certain instances is the readiness with which the pelletswill alloy with the molten metal in the mold if the two come intometal-to-metal contact. Such alloying is to be avoided or minimized.

The metal portion of the chill mixture constitutes the largest partthereof, at least 85 per cent of the total weight being made up of metalpellets, but at least 90 per cent is employed in my preferred practice.The size of the metal pellets has an important bearing upon theirutility. I have found that if the pellets are larger than 30 mesh, theyare not satisfactorily held in place by the usual binders, and they alsotend to produce a rough surface on the casting. On the other hand, ifthe pellets are smaller than 150 mesh, a large part of the chillingcapacity of the mixture is lost and the disadvantages of metal dust orpowder are encountered. I have also found that the best results areobtained by using substantially spherically shaped bodies of metals.Pellets oi the foregoing size and shape are frequently referred to asshot. The term, pellet, as herein employed, however, is intended todescribe rounded and substantially sphericai'bodies and includes metalparticles of 30 to 150 mesh size known in the trade as grit.

Although pellets of a single mesh size may be used in a chill mixture,better results are obtained if two or more mesh sizes are employed. Forexamplaa combination of 40 and 60 mesh pellets are better than 40 or 60mesh pellets used separately. In some instances it is advantageous touse three mesh sizes of pellets, for example, 40, 60, and 90.

The binder portion of the mixture may consist of any of the common greenor dry binder materials on the market so long as the chill mixture hasthe desired degree of cohesion and resistance to crumbling when exposedto the molten metal in the-mold. A binder that is particularly usefulwhere chills are used in green sand molds is a bonding clay such asbentonite. This type of binder generally does not harden and hence achill mixture containing such a binder is in a green condition when usedas a chill. Chill mixtures containing this binding material can berammed in the molds in the same manner as molding sand, and theresulting product is then handled as any other green sand mold. Afurther restriction on the choice of binder is that in cores it shouldnot yield enough g s during the casting operation to form blow holes.Although thermosetting synthetic resins find some application in Q greensand molds, they are especially useful as binders in my chill mixturewhen used in baked sand cores because a smaller quantity is needed tohold the metal pellets in place, than where other types of core bindersare used, and they produce but a very small amount of gas in the mold.This relative freedom from gas production is highly important in makingcastings of metals which are sensitive to gas, for example, magnesiumbase alloys. In general, from 0.5 to 3 per cent by weight of the chillmixture may consist of the synthetic resin. A large number ofthermoset'ting resins are on the market which are satisfactory for thispurpose, but I prefer to use at least one substance of the groupconsisting of the urea formaldehyde and phenol formaldehyde types ofresins. Where other types of binders are used in either green sand moldsor cores, from 0.5 to as much as 5 or 6 per cent may be required toobtain the necessary bond.

In making up a green chill mixture the pellets and binding material aremixed together so that there is a uniform distribution of binderthroughout the metal mass. The mixing may be conveniently accomplishedin a muller. Enough water or other aqueous or non-aqueous temperingmedium should be added to provide the right degree of moldability. Inmaking green chill mixtures containing iron pellets, it may be desirableto use a dilute aqueous solution of l per cent potassium dichromate orpotassium permanganate, as the tempering medium, to prevent rusting.Other rust or corrosion inhibitors may be employed, of course, thechoice in any case depending on the metal composing the pellets and theconditions favoring corrosion.

Once the green chill mixture has been prepared, it can be placed in themold next to a pattern or in the core box and the remaining sand whichconstitutes the mold or core can be placed behind the chill and thewhole mass rammed in the usual manner. In cases where dried sand coreare to be made, the same molding procedure may be followed, but thegreen cores are baked in order to give them the required strength andfreedom from moisture in the final mold. The green chill mixture hereindescribed has been found to be particularly useful in green sand mold inwhich aluminum base alloys are cast. The reference herein to lightalloys is intended to include both aluminum and magnesium and the alloysin which these metals predominate.

Minor amounts of other substances than those enumerated hereinabove maybe present in the chill mixture either as impurities or as intentionallyadded components. For example, where magnesium alloys are being cast,especially in green sand molds, it is necessary to include well knownoxidation inhibitors-such as boric acid and/or diethylene glycol in themixture in amounts, for example, of 0.5 to 3 per cent by weight of themixture. The added components should not, in any event, materiallyreduce the chilling effect of the mixture, nor should they adverselyaffect the moldability of the green mixture. Molding sand, however,should be excluded from the chill mixture because of its adverseinfluence upon the chilling effect. In referring to the chill mixtureinthe appended claims as being substantially composed of metal pellets,a binder, and a tempering medium, it is intended that other substancesof the kind Just enume ate shall not be excluded so long as theessential characteristics of the mixture are retained.

An example of a chill mixture which gives satisfactory results incasting light alloys is one consisting of 150 pounds of 60 mesh ironpellets, 150 pounds of 90 mesh iron pellets, 6 pounds of bentonite, 6pounds of cornstarch and enough 1 per cent potassium dichromate aqueoussolution to temper the mass. useful for chills in green sand molds.Another mixture which is particularly useful in baked sand cores is oneconsisting of 150 pounds of 60 mesh iron pellets, 150 pounds of 90 meshiron pellets, 1.75 pounds of urea formaldehyde, 1.75 pounds of phenolformaldehyde, and enough 1 per cent potassium dichromate aqueoussolution to temper the mass. The water in the mixture is of courseremoved by the baking, thus leaving a hard chill mass.

I claim:

1. A chill mixture containing atleast 85 per cent by weight of 30 to 150mesh size metal pel- This mixture is especially lets, a bindingmaterial, and a tempering, medium containing a corrosion inhibitor, saidmixture casting in the region of the chill as compared to the conditionprevailing in the absence of said chill. Y

2. A chill mixture for use in green sand molds for the-casting ofmagnesium base alloys consisting of at least 85 per cent by weight of to150 mesh size iron pellets, 0.5 to6 percent by weight of bentonite, 0.5to 3 percent by weight of an oxidation inhibitor, and a temperingmedium'containing an iron rust inhibitor, said chill mixture beingcharacterized by being moldable and having a chilling efiect suflicientto reduce the grain size and shrinkage in the casting in the region ofthe chill as compared to the condition prevailin in the absence ofsaidchill.

A chill mixture for use in green sand molds consisting of at least percent by weight of at least two different sizes of 30 to mesh size ironpellets, 0.5 to 6 per cent bentonite, and a tempering medium containingan iron rust inhibitor, said chill mixture being characterized .by beingmoldable and having a chilling effect sufllcient to reduce the grain izeand shrinkage in the casting in the region oflthe chill as compared tothe condition prevailing in the absence of said chill.

' MARVIN E. GANTZ.

